The invention relates to a pulse generator comprising at least two voltage comparison circuits and having an input for receiving a variable input voltage and an output for supplying pulses having pulse edges occurring at instants at which the instantaneous input voltage value is substantially equal to one of at least two threshold values to be supplied by a voltage source and present at the voltage comparison circuits.
Such a pulse generator is disclosed in U.S. Pat. No. 3,711,642, the pulses being used to obtain equidensity lines in a picture obtained on the display screen of a display device under the control of said input voltage. In said patent the pulse generator comprises diodes which are biased to different threshold values from the voltage source, which diodes become conductive when the varying voltage is applied to them, at the instants and result in conjunction with switches controlled thereby in the pulse generation.